In the scene, one can see Clark's thought process. He only recalls his kiss with Wonder Woman when he's trying to convince himself he's moved on. He seems to be genuinely surprised at how much seeing Lois getting closer to Jonathan still bothers him despite the fact that he's kissed another woman. He's basically attempting to remind himself that he shouldn't care or feel hurt at all because he's got someone too. This bothers me because it suggests that while he's getting closer to Diana, his hope is still that Lois would want to be with him. So if, for example, this scene had played out differently and the text from Jonathan would have been about he and Lois breaking up, and then later Lois would have given Clark reason to hope for something more between them, he would have quickly thrown cold water on anything happening with Diana because she's not who his heart really wants; because, again, he hasn't gotten over Lois yet. It's not wholly unusual for this type of thing to happen, but it is messy, and it is discomfiting to think of Clark being an emotional coward where Lois is concerned and unfair where Diana is concerned.